This proposal is concerned with a broad study of the mechanisms which control the interplay between conformational changes, ligand binding, non-specific solvent effects and self-assembly in biologically significant systems. Thermodynamic, kinetic and conformational studies will be carried out in rigorous manner of the detailed mechanism of the self-assembly of purified brain tubulin to microtubules, with particular emphasis on the manner in which certain ligands, such as calcium and magnesium ions, control the assembly and disassembly of microtubules on the molecular level, the manner in which the GTP-GDP system modulates the stability of the assembled organelles, the linkage between ligand binding, conformation changes and assembly, and the identification of possible assembly intermediates. Also studies will be carried out on the mechanism by which some solvent additives (such as sugars, salts and glycols) stabilize biological structures and affect the activity of enzymes, on the relation between the fine structure of proteins and their biological function, and on the conformational pathway in which such active structures are generated during enzyme activation. The methods used will be those of macromolecular physical biochemistry, such as sedimentation, specrofluorometry with energy transfer, densimetry, quantitative gel chromatogrpahy and light scattering, as well as controlled chemical modification. This research is aimed at the problem of the complex interplay of non-covalent interactions and biological function and the eventual understanding of how organelles are assembled and stabilized within cells and of the manner in which extraneous substrates, such as carcinogenic materials and drugs, perform their action.